[dyarosla]

Extrapolation is one of those ideas that’s not actually used in practice- at least I’ve yet to see it used in any games in any meaningful capacity.

It’s just far too complicated and requires custom logic while resulting in worse results than more straightforward options. Even for multiplayer games the “extrapolation” is often done by repeating input states and running the regular game loop.

I also wouldn’t equivocate the interpolation approach with extrapolation. With interpolation you interpolate between two valid states. With extrapolation you produce a potentially invalid state (ie a character that’s inside of a wall). The only work around for the latter issue is to perform a full game tick - at which point you’re no longer doing extrapolation.

[jayd16]

> Extrapolation is one of those ideas that’s not actually used in practice

This is how VR frame doubling works, no? "Timewarp"/"Spacewarm"

Also I would think that a lot of netcode would be considered extrapolation. You'd extrapolate a peer's input or velocity (and perhaps clean it up with further local simulation) and then deal with mis-prediction when changes are replicated.

[dyarosla]

For the former, Timewarp is used at an OS level to perturb the visibly rendered quad to match the display time orientation. There’s no extrapolation: the rendered frame is simply adjusted to account for the change in headset orientation.

For the latter, as I mentioned, the extrapolation is not on velocity: you still compute regular game ticks but by holding the input constant. This is quite different from extrapolating velocities.

[jayd16]

Spacewarp takes the motion vectors and depth buffer and generates new frames from the extrapolated motion. Its detailed here. https://developers.meta.com/horizon/blog/introducing-applica...

> For the latter, as I mentioned, the extrapolation is not on velocity: you still compute regular game ticks but by holding the input constant. This is quite different from extrapolating velocities.

Replicating velocity is fairly common. Unreal's character movement replicates velocity and not inputs. I would personally argue that even doing a full game tick with replicated velocities is extrapolation. I'm not sure what the distinction would be or what counts as a full tick with error correction vs local extrapolation per tick with error correction.

[dyarosla]

I agree- what’s the difference between error correction and a full tick? At what point do you draw the line on error correction?

Extrapolation is often used to mean extrapolating values without error correction, at which point the results are less than stellar.

Spacewarp is, like Timewarp, a way to match the render frame time on a headset but by creating a warp of the output image; ill concede that this is technically extrapolation but is far away from whats generally referred to in describing updating entity values in game loops.